The invention concerns an electromechanical energy converter designed as a linear generator having a free piston.
In contrast to conventional electromechanical energy converters, linear generators with freely oscillating working pistons dispense with rotary movements and the crank drives needed for these. The energy conversion is provided by the back and forth linear movement of a working piston, often known as a free piston. The conversion of the mechanical energy into electrical energy takes place thereby that the working piston is provided with a plurality of magnets of alternating polarity and is arranged in a coil surrounding it (DD 113 593, DE 43 15 046 A1, DE 199 43 993 A1). A corresponding principle is applied to electromechanical converters that do not work as electrical generators, but as electrical linear motors (DE 41 07 530 A1) or that serve optionally for electrical or mechanical energy generation (EP 0 185 656 B1). Due to the plurality of permanent magnets mounted on the working piston and the inertia caused thereby, large accelerating and braking forces have to be applied, which result in low working frequencies. Normally for these so-called field displacers, magnet pairs arranged with mirror symmetry or rotational symmetry are used, in order, in the ideal case, to avoid lateral forces. Due to manufacturing tolerances, this is not fully achievable, however and the bearings are increasingly loaded through even the slightest wear. These loads then become exponentiated. Complex designs increase the proneness to faults, which militates against maintenance-free operation of the working piston over several years.
Energy converters of the aforementioned type have therefore become known (U.S. Pat. No. 4,532,431, WO 94/26019) whereby the working pistons are linked solely by a coreless armature coil, displaceably mounted in the air gap between two pot-shaped stator members arranged mutually opposed. Although an arrangement of this type offers significant advantages with regard to the accelerating and braking forces to be applied, energy converters of this type have previously not become established on the market. A main reason for this may be seen in the fact that the piston heads impinged upon by the gaseous or vaporous medium are displaceably mounted in chambers arranged outside the stator, whereby sealing problems arise which militate against operation of the piston free from faults and servicing over several years. Furthermore, it is not possible with these energy converters without further difficulty to guide the gaseous or vaporous medium round a circuit, to realise a compact and space-saving design, and to solve cooling problems arising during operation.